Telephone receiver



July 18, 1950 c. A. MAYNARD 2,515,414

TELEPHONE RECEIVER Filed Sept. 8, 1947 2 Sheets-Sheet l FFL-.5121.

July 18, 1950 c. A. MAYNARD 2,515,414

TELEPHONE RECEIVER Filed Sept. 8, 1947 2 Sheets-Sheet* 2 Patented July18, 1950 TELEPHONE RECEIVER Charles A. Maynard, Valparaiso, Ind.,assignor to The Indiana Steel Products Company, Chicago, Ill., acorporation of Indiana i YApplication September 8, 1947, Serial No.772,696

This invention relates to a telephone receiver, and more particularly tothe magnetic circuit for a telephone receiver.

One of the' principal features and objects of the present invention isto provide a telephone receiver construction having an improved magneticcircuit and employing high coercive force permanent magnet material.

It is a further` object of the present invention to provide a novelheadphone of the polarized type wherein the magnets have relativelyshort magnetic lengths, but relatively large cross-sectional area.

A still further object of the present invention is to provide ya novelelectromagnetic transducer head for changing fluctuating electric energyinto sound.

Another and further object of the present invention is to provide anovel `telephone receiver structure in which the magnetic yoke whichprovides the return ux path for the short permanent magnets also acts asthe main support for the complete assembly.

'Ihe novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization, and 'mannerl ofconstruction, together with yfurther objects and advantages thereof, maybest be understood byv reference to the vaccompanying 3 drawings, inwhich:

"Figure l isa vertical sectional view through a telephone` receiverembodying the novel characteristics andv principles of the presentinvention; ,v

Figure 2 is an isometric view of the magnetic circuit and the operatingsignal coils of the recever shown in-Figurel, with a` portion of onecoil broken away; i

Figure ,3 isyagvertical sectional'view of a modied form of telephonereceiver; and

Figure 4 is an'isometric view'of the magnetic circuit andelectricalcoils of the modied form of the inventionshown in Figurel 3.

Referringrst to, the form 'of the invention shown in Figures 1 and 2 oflthedrawings'the telephone receiver I includes a housing I I ofnonmagnetic materialhaving 'a perforated cap I2 which is arranged toclose-the open end thereof. A metal-inner shell or housing I3 ofynon-magnetic material is provided as the main Support Afor theassembly...-The housing, I I .has a'threaded upper end I4 which isarranged to receive the downturned outer` flange I 5rof` the cap `I 2.

As may be seen'` .best in Figui'eZof the draw- 6 claims. (o1. 17a-,1114)ings, the magnetic circuit of the receiver Ill includes a pair ofpermanent magnets I6 and I'I whichare secured to a U shape yoke memberI8 of soft iron or other suitable magnetic material of relatively` highpermeability but low retentivity. The permanent magnets IB and I1 arearranged so that the Vsouth pole of one of the permanent magnets is up,such, for example, as the magnet I6, while the north pole of the otherpermanent magnet, such, for example, as the magnet I 1, is uppermost. p

A pair of L-shaped pole pieces I9 and 20 are secured to the lower endsofthe permanent magnets I6 and I'I, respectively, suitable bolts 2| and 22being 'employed to secure the assembly of the yoke I8, the permanentmagnets I6 and I1, and the pole pieces I9 and 2t) together. The L-shapedpole pieces I9 and 20 extend inwardly and then upwardly to a level justslightly above the yoke I8.

A pair of signal coils 23 and 24 are mounted over the upstanding legportions of the pole pieces I9 and 20.

The assembly, as shown in Figure 2, is mounted in the housing II (seeFigure l) and a diaphragm 25 is clamped by the, shoulder 26 on the capI2 vagainst the upper rim of the inner housing'or main support memberI3. The diaphragm 25 extends across the housing II in a conventionalmanner, and is disposed in a position just slightly spaced above -theupper ends of the pole pieces I9 and 20. Thediaphragm 25 is, of course,a thin circular diaphragm of iron or other suitable magnetic material4having relatively high permeability and relatively low retentivity, andthe center of this diaphragm is drawn toward the pole pieces I9 and 20under some tension. When an alternating current'flows through the coils23 and 24, the 4field set up by the current alternately aids and opposesthe steady .field set up by the permanent magnets I6 and AI'I so thatthe diaphragm 25 is alternatelydrawn nearer to and allowed to springfurther away from the pole pieces I9 and 20. V

It has beenrfound that greatly improved results can be received in atelephone receiver and a better response characteristic maintained byusing short permanent magnets of extremely high energy product such,forv example, as an energy product of 4 or 5 million.

It has further-been found that when .a pail oi such permanent magnetsare employed in conjunction with a return fluxI path for the permanentmagnets in theV iorm of a magnetic vyoke and then pijovidingapair-ofL-shaped soft iiron side in order that the various elements may bei moreclearly shown.

In this form of the invention, the L-shaped pole pieces I9 and 2U aresimilar tothosedis cussed in the rst form offtheinventionfa-nd aref-.v`secured to the ends of the permanent magnets IB" and l1, which areopposite tothatto-,Whichthe circular magnetic yoke 21 is secured. Thesignal coils 23 and 24 are mounted on thev verticallyA extendingportions ZB-and 29 of the L-shaped polemembers {wand-l 291iI `In' this;form otfithe invention theiinnerhousingnl' of tlieiirstform oi 'theinventiond'iaslbeeni. eliminated',- and S only the. outer housingfmember3U with itsiassociated cap 3| is. provided?4 for,I the magnetic circuit.of the' electric sig-nal?coils;v

The housing 30`ihas :a seat: or lshoulder portion 32`thereon uponvvh'ich'fisiy seated ther circular yoke 2T. i This yoke f 21 has: anupwardly." extending outer fiange' portion or-lipl 33'upon which isseated the diaphragm@ The'cap member 3i isL provided with` an ir'inerryshoulder` '31T which, wheny the cap'isr screweddownonto 'the lowerhousing-- member 392, forcesthe--outer7 edge of the diaphragm FtiglitlylagainstA the: lipA 33=`of the yoke-2lii and thus,-A in turn; forces theyoke 21 tightly-'against theshoulder 32: of the lower housinge memberV391': It lwilltlfn'is'v be seen that? the yoke-2?l-acts.as-tlfieJ-main- Support for? all'of the interiorl-meclnanismf,l botlfrmagnetic `and electrical, of theereceiver; The! circular yoke yorvannulu's 2'! which is of soft iron or other suitablefmagnetic material,`thus `provides a. dual". return luxzxpath for-the permanent`magnets-@I(il vand;et`l.,-*one` of i thesefcircular paths being: thesemi-circularfportion l'which' lies 1 to one: sidelfot ftheV permanentmagnetsV lland il, andthez other-orparallel fluxflpathI isthroughthe.otherf'semiL-circular por;- tier-133 of the yoke-21 wlrichtliesto-the'otherr side of the permanent inagnetsiL l 6 and 'I 'le vIn lthisembodimentlofilthei presenti invention, as-wellas in the -rstemb'odimentzoifthe'present invention; the.. completeifma'gneticfcircuit' Lis from thelnOrth pole of onefperm'anentumagnet;throughthecyoke to thel-southpole offtli'eV other permanent magnet, thenffromfthe-northfpole of:th.is second permanentv mag-netg threughthez=`softfironi L- shapedpole piece 'to1`thesoft iron diaphragm, through-rYthefV diaphragminto: the: f L'sl1aped. pole piecerof the: Erst fpermanent fmagnet andfrom there-into the: south pole v of .-the, ifrst.lpermanent magnetr- It` will` thusfbe apparent-that a.very efficientmagnetic circuit is provided.

It-v will further be observedlthat, by the Vfuse of .verycoerciveforcepermanent.. magnet materialspermanent magnets may be employed whichare of relatively shortv magnetic lengths, but of relatively largevcross-section, thereby to keep the receiver small' and compact;

The term electromagnetic transducer will hereinafter be-used :torefer toa telephonefreceiver or head set'whicliis arrangedto. convertfluctuating energy ofionel-form` into fluctuating energy ofanotherdorm-such, forvfex-am-ple;t as iluctuating electricene'rgy..i1"i"to`'sounds'` While I have shown certain particularembodiments of my invention, it will, of course, be understood that manyother modifications may be made embodying the teachings and principlesof the present invention.

I claim as my invention:

1. An electromagnetic transducer comprising a pail` of permanentmagnets; mounted in side by side spaced relationshipwith their magneticaxes substantially parallel and oriented in opposite directions, arelatively thin curvilinear yoke of magnetic material of high magneticpermeability Vbut low magnetic retentivity secured to each of onesetrofendsof said permanent magnets, a pair orpolepieces-extending from theother set of ends of saidl permanent magnets, a resilient ferromagnetic:diaphragmxmounted in closely spaced relation to the free ends of saidpole pieces, and signal coils on said pole pieces.

2. An electromagnetic transducer comprising a pair-oi 2 permanent'magnetsfl mounted' in side by side :spaced Irelationship with` theirmagnetic axes substantially parallel and oriented 'in oppositedirections, ,i a. relatively. thin' curvilinearyoke of vmagneticmateriallfofhigh magnetic permeability 'but`L low-f magneticsretentivity: secured to each of 'one set-of endsiovsaidfpermanentmagnets, a pair of L-shaped pole pieces,.e'xtendingiirsttoward `eachother ands'thenrupwardly between said permanenti.magnets ,and i connected respectively to th'eendsioi salidt'permanentmagnets` s0 as to. lie opposite -to'-tliiattorY which -isaid yoke Yisconnected, a resilient ferromagnetic diaphragm mountedf'incloselyfspaced-'relation to thewfree endsof said 'polelpiecesand' signalcoils mounted on said" pole pieces.

3. An electromagnetic transducer comprising azpair of permanent. magnetsmounted in side byside spaced? relationship with theirl magneticAaxesiY'si'ib'sta'ntiallyl` parallelI and oriented in opposite@directions, ai relatively thin curvilinear yokeoffmagnetic materialothigh magnetic permeability but low magneticf'retentivity secured toeaclif of oneI setof ends of' said permanentfmagnets, a` pairf'o'fL-shapedipole pieces extending rstftowardfeach other'and then upwardlybetween` 'said permanentf magnets. and" connected respectivelytomtheends of said-permanent magnets-as to lieopposite'to that'to whichsaid yoke is 1 connected', a` resilient ferromagnetic diaphragm mountedin closely'spaced relation to thef'ree ends of said pole pieces'andsignal coils mountedon said pole piecesythe free endsf ofsaidpolepiecesi terminatingI in a? plane slightly above the plane of theupper surface of said yoke.

4: An'electromagnetic'transducer comprising a pair of permanent lmagnetsmounted inside by side'spacedrelationship andoriented oppositeldirections, av U-shaped ferromagneticL yoke secured to the-'upperends"ofsai'd permanent magnets and providihg-Famagnetic paththerebetween, a pair "ofLl-shaped'pole; members offerromagneticmaterialsecur'ed'to 1' thelower ends y terial, a cap havingopenings therein for closing the open end of said housing, aferromagnetic yoke member in the form of an annulus, a pair of permanentmagnets secured to diametrically Y opposite portions of said annuluswith their magnetic axes perpendicular to the plane of said annulus andoriented in opposite directions with respect to each other, a pair ofL-shaped pole pieces secured to the opposite ends of said permanentmagnets and extending rst toward each other and then upwardly betweensaid permanent magnets and through the central opening of said annulus,a pair of signal coils mounted on the upwardly extending portions ofsaid pole pieces, said annulus being secured to said housing and actingas the sole support for the magnetic and electric circuit of saidtransducer, and a ferromagnetic resilient diaphragm secured in closelyspaced relation above the free ends of said pole pieces.

6. An electromagnetic transducer comprising an open-ended housing ofnon-magnetic material, a cap having openings therein for closing theopen end of said housing, a ferromagnetic yoke member in the form of anannulus, a pair of permanent magnets secured to diametricallyoppositevportions of said annulus with their magnetic axes perpendicularto the plane of said annulus and oriented in opposite directions withrespect to each other, a pair of L-shaped pole pieces secured to theopposite ends of said permanent magnets and extending rst toward eachother and then upwardly between said permanent magnets and through thecentral opening of said annulus, a pair of signal coils mounted on theupwardly extending portions of said pole pieces, said housing having aseat for receiving said annulus, a resilient ferromagnetic diaphragm,said annulus having a seat for said diaphragm, and said cap beingarranged to secure said diaphragm and said annulus against said annulusseat of said housing whereby said annulus provides the sole support forthe complete assembly as well as providing a return ux path for Saidpermanent magnets.

CHARLES A. MAYNARD.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,414,105 Timmons Apr. 25, 1922)1,530,323 Pratt Mar. 17, 1925 1,537,322 Nielsen May 12, 1925 1,624,338Hanna Apr. 12, 1927 2,249,158 Morrison July 15, 1941 2,353,550 DeForestJuly 11, 1944

